Metalworking fluid compositions are well known in the art and function to lubricate and cool various metallic surfaces during metalworking operations such as cutting, turning, drilling, grinding, quenching and the like. For example, U.S. Pat. No. 4,129,509 discloses the use of a fluid emulsion containing a mineral oil and water. In order to stabilize the oil and water emulsion against attacks from bacteria and against degradation due to the metalworking conditions, the patent suggests the addition of an emulsifying agent and a metal complex of a heavy metal ion and a polyfunctional organic ligand. However, cutting fluids containing mineral oil cause problems when used for the machining of metals due to the formation of undesirable non-settling and highly viscous sludge in storage tanks, pumps and tubing. The presence of emulsifying agents aggravates this problem further. Thus, it is well known in the art that, for this reason, cutting fluids containing mineral oil are particularly unsuitable for use in the machining of cast iron, which produces large amounts of particulate contaminations.
Mechanical working of cast iron, especially of the quality usually called nodular or spheroidized graphite iron, is often performed in the presence of aqueous oil-free metalworking compositions such as the ones disclosed in U.S. Pat. No. 3,265,620. In connection with such compositions, however, a poisonous gas is generated, i.e. phosphine. The generation of phosphine is due to the fact that cast iron contains carbon (graphite) with inclusions of phosphorous material. When machining cast iron in the presence of water, this phosphorous material reacts to form phosphine.
To reduce the generation of phosphine it has been suggested, e.g. for cutting operations, to use metalworking compositions containing potassium permanganate which is a strong oxidizing agent. While this method has proved to reduce the generation of phosphine, the consequences have been severe corrosion attacks on machinery, tools, and machined iron. Furthermore, the compositions containing potassium permanganate are not stable, resulting in precipitations, primarily in the form of manganese ore.